jit.qt.movie+asyncread audio problem

When using asyncread the volume does not get to full level if a movie file was
loadded before
with a level below 1.

Steps to reproduce:

1) use jit.qt.movie.help
2) change read to asyncread
3) asyncread a movie
4) start playing and scroll the volume to for ex. to 0.09
5) asyncread another movie (you can also stop the running movie before)
6) start playing the movie
7) Now try to scroll the volume of this movie to full level-> level stays around
the previous
level